Vinews Viticulture Information News, Week of 13 June 2016 Columbia, MO

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1 NO. 6 1 Vinews Viticulture Information News, Week of 13 June 2016 Columbia, MO Captan Warning As you transition from mancozeb containing products to Captan be aware of potential phytotoxicity. Phytotoxicity although rare, often appears when Captan is mixed with oils. When Captan is mixed with spray oil, adjuvants and emulsifiable concentrates these act as penetrants and the Captan can move into the grape and tissue. This results in leaf spotting and the injury is more apparent on young unfolding leaves that have limited cuticle. The injured tissue provide an opportunity for other pathogens to infect. There are a few emulsifiable concentrate (EC) pesticide formulations that you want to avoid mixing with Captan. Never mix Danitol 2.4EC, Mustang Max 0.8EC, Baythroid XL (1EC), Onager 1EC, Portal 0.4EC, Brigade 2EC, Agri-Mek 0.15EC, and Pyganic 5%EC. Also avoid mixing Captan with organophosphates such as Lorsban Advanced and Malathion 8F. These products contain petroleum distillates of which some distillates maybe oils. Captan 50 WP Label Do not apply Captan in combination with or immediately before or closely following oil sprays. Captan phytotoxicity can result if oils were applied prior to or after an application of Captan. The use of spreaders, which cause excessive wetting, is not advised. Combinations with solvent formulations of organic phosphates should not be used. applications during warm, cloudy, humid weather should be avoided

2 2 Sulfur Warning Some grape cultivars are sensitive to foliar sulfur application. Sulfur is often applied to manage powdery mildew. The following grape cultivars are sensitive to sulfur. Cultivars Sensitive to Sulfur Chambourcin Chancellor Concord DeChaunac Foch Leon Millot Norton Sulfur phytotoxicity from sulfur on Leon Millot. Dry sunny conditions with temperatures over 90 F slow many grape pathogens Black rot needs a minimum of 12 hours of wetness for infection when the temperature is 90 F. In comparison only 6 hours of leaf wetness are needed when the temperature is 80 F Downy mildew produces no sporangia when temperatures are above 85 F Powdery mildew spores and colonies can be damaged by temperatures above 91 F. When temperatures rise above 95 F for 12 hours or more powdery mildew can be completely destroyed Phomopsis would need greater than 20 hours of leaf wetness at 95 F for infection to occur

3 3 Pestalotiopsis Appears Again but as a Leaf Disease Last year about this time, I reported on a fruit rot that was the result of Pestalotiopsis. Some like to refer to Pestalotiopsis as Pestalotia but they are different. Pestalotia, Pestalotiopsis, and Truncatella are three separate genera categorized based on conidial form. Pestalotia species include 6-celled conidial forms, Pestalotiopsis species include 5-celled conidial forms, and Truncatella species have 4-celled conidia. Pestalotiopsis produces small cushion reproductive structures called acervuli that contain pycnidia that produce pigmented conidia. The conidia of different species are classified based on conidial appendages that may be branched and differ in number. Most of the classification of Pestalotiopsis and related genera to species level is done through DNA analysis. Pestalotiopsis spp. have been reported to cause leaf lesions, fruit rots, and have been found as trunk diseases in Arkansas and Missouri. The Pestalotiopsis sp. discovered last season was causing fruit rots in the grape cultivar Norton (Figure 1). This season, I have received reports of leaf discoloration in both Norton and Chambourcin (Figure 2). Initially, I believed that the discoloration being observed was from angular leaf scorch. After incubating surface sterilized leaves in a moist chamber, Pestalotiopsis was observed. Pestalotiopsis can develop just beneath the plant cuticle (subcuticular) or within the epidermal layer (intraepidermal), or just below the epidermal layer (subepidermal). Pestalotiopsis can live within a plant for a portion of its life cycle without causing any disease, therefore Pestalotiopsis is classified as an endophyte. As a pathogen, Pestalotiopsis is opportunistic and the pathogenic stage can be triggered by a number of factors, plant susceptibility, environmental conditions, and the virulence of the pathogen. At this point, we do not know what combination of factors is triggering disease. Leaf lesions from Pestalotiopsis were observed only on leaves so far this season. Leaves showing symptoms were collected from Chambourcin grape plants in New Franklin, MO and Cuba, MO. At the Cuba site some leaves had turned a dull brown/green or become completely necrotic and dropped from the vines when samples were collected on May 13. Leaves were collected at the New Franklin site on May 15. The symptoms on the leaves at both sites were on younger, not fully expanded leaves. Leaf samples were moist incubated and oozing pycnidium (Figure 3) were observed. Within these pycnidium were 5- celled pycnidiospores of the fungus Pestalotiopsis (Figure 4). Figure 1. Disease symptoms of Pestalotiopsis sp. causing fruit rot in Norton in Figure 2. Disease symptoms of Pestalotiopsis sp. causing leaf discoloration in Chambourcin during May 2016.

4 4 On June 6, I was contacted by a Minnesota grape grower that had recently planted Norton vines and the leaves were showing according to the grower a pink/red discoloration (Figure 5). The grower sent me some leaves and moist incubation was completed and Pestalotiopsis was also found in these samples. What is striking is the symptoms are very different between Chambourcin and Norton. Also the pycnidium oozing from a nida from the pycnidium Figure 3. Pestalotiopsis Figure 4. The 5-celled co- leaf samples produced oozing pycnidium whereas the bourcin grape leaf. moist incubated Cham- are Pestalotiopsis. fruit rot sample from last year did not which suggests that a different Pestalotiopsis species may be involved. A B C Figure 5. Pestalotiopsis sp. leaf symptoms on Norton vines from Minnesota. Early lead symptoms caused pinking (A) followed by necrosis (B) resulting in leaf vein collapse (C). In two of these cases, Chambourcin from the Cuba site and the Norton from Minnesota had not received a mancozeb application when symptoms first appeared. At the New Franklin site mancozeb had been applied and symptoms did appear. At both the Cuba and New Franklin sites the leaf symptomology is no longer present. The Minnesota Norton vines were just recently treated with mancozeb and I will report back on the outcome. Since Pestalotiopsis can also cause fruit rots the go to fungicides would be strobilurins (Pristine, Abound, Flint) and mancozeb. Remember the PHI for mancozeb is 66 days.

5 5 Downy and Powdery Mildew Often confusion exists in identifying grape diseases based purely on appearance. This is especially a true for Downy and Powdery mildew that appear to the naked eye to have similar colored and structured mycelium (dense downy or powdery growth). Determining which mildew problem is impacting your vineyard is important since a number of fungicides only control powdery or downy mildew. The goal of managing both powdery and downy mildew is to prevent an infection from occurring. Often however, either powdery or downy mildew infections occur even with the best disease management programs. This may result from a sprayer malfunction, weather events prevented timely applications of fungicide cover sprays, large rainfall events washed off protective sprays from grape tissues, or poor spray coverage. Regardless of the reason why an infection occurred, management of the disease is dependent on identifying the causal agent and applying a control strategy. Scouting and Risk Hot dry weather increases the risk for powdery mildew infection. Scout for powdery mildew in shaded areas within the canopy and vineyard border rows shaded by trees. Regional MU Horticulture Research Specialists have reported powdery mildew on grapes in the Kansas City area this week. Identifying downy or powdery mildew based on plant symptomology The disease symptoms that first appear on grape tissue are different for downy and powdery mildew. A downy mildew infection on leaf tissues results in yellow, chlorotic, oily spots that appear on the top surface of the leaves. These oil spots will appear different on different grape cultivars based on the susceptibility of the cultivar to downy mildew. For example, on the highly susceptible cultivar such as Valiant the oil spots are typically larger compared to oil spots that appear on a more resistant grape cultivar such as Norton. If the infection has progressed, a white mycelium or downy patches develop on the bottom of a leaf. Downy mildew will only form white mycelium or downy patches on the bottom of the leaf since that is where stomata are located. The stomata are where downy mildew starts the infection process. Grapes leaves do not have stomata on the top surface of the leaves unless the leaves are galled by foliar phylloxera. Foliar phylloxera takes over the grapes physiological processes and this results in stomata forming on the top surface of grape leaves. These stomata on the top surface of grape leaves can result in downy mildew infections and the development of downy mass on the top surface of grape leaves. Obviously this compounds the problem of identifying powdery or downy mildew in vineyards that are also impacted by foliar phylloxera. The first symptoms of powdery mildew that are visible are the white mycelium or powdery patches that can occur on either the top or the bottom of a leaf. If you see white mycelium or powdery patches on the top of the leaves then you likely have powdery mildew. When scouting for powdery mildew, look at leaves within the interior of the canopy that are shaded. The powdery mildew fungus seldom will be found on leaves directly exposed to intense sunlight since sunlight is detrimental to powdery mildew. A sure way to differentiate downy mildew from powdery mildew is to exam the fruiting structures using hand lens or a compound microscope. Downy mildew fruiting structures look like a small tree with several branches and attached to these branches are single, round spores or sporangia. In comparison, powdery mildew will have a single stalk (conidiophore) with several barrel shaped spores (conidia) stacked on top of each other (See next page for pictures).

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7 7 Comparison of downy and powdery mildew Site of infection Environmental conditions for infection Powdery mildew (A) Both sides of leaf (B) Grows on leaf surface (A) High humidity but moisture such as rainfall detrimental to spores (B) Optimal (68 to 77 F) but ranges (59 to 90 F) (C) Low diffuse light conditions favor development Downy mildew (A) Only infects bottom of leaf (B) Grows inside of leaf (A) High humidity and free moisture in the form of rainfall or dew needed for infection (B) Optimal (64 to 76 F) but ranges (54 to 86 F) Tissue infected (A) All green tissue (B) Berries susceptible until 3 to 4 weeks post bloom (C) Leaves and green tissue susceptible throughout season Spore transmission Wind Splashing water Symptoms (A) Circular spots that are not limited by leaf veins (B) Advanced infections will cover leaves with thick web of spores, leaves turn yellow and may fall off (C) Spores produced in a single chain on a single stalk (A) Angular spots that are limited by leaf veins (B) Grey/white fuzz on undersides of leaf, top of leaf has yellow blotches that look oily (C) Spores produced singly on end of branched stalks Potential problem periods Highly susceptible grape varieties Management Cultural Essential Management Period Dry periods during the growing season Chambourcin, Seyval, Vignoles, Vidal blanc (A) Reduce shading in canopy by; 1) shoot positioning and 2) leaf removal Wet periods during the growing season Catawba, Vinifera cultivars (A) Reduce tissue wet period by: 1) site selection, 2) vine spacing, 3) control tall weeds, 4) shoot positioning, and 5) leaf removal (B) Sanitation remove fallen leaves and fruit from vineyard Start of bloom to 4 to 5-weeks post bloom. Use the best fungicides within your budget for immediate pre-bloom to post bloom

8 Downy mildew can take many forms and at times may appear more like powdery mildew as in the case with diffuse downy mildew. 8 Typical Downy Mildew. Photo credit: Patty McManus, UW-Madison. Diffuse Downy Mildew. Photo credit: Patty McManus, UW-Madison.

9 Downy mildew can cause infection only where stomata are present. Grape leaves only have stomata present on the bottom surface. However, when grape leaves are galled by foliar phylloxera, this results in stomata forming on the top surface of grape leaves. This presents another avenue for downy mildew to infect grapes as the galled leaves show below. 9 Downy Mildew There are a number of fungicide options to protect grapes from downy mildew. See page of the 2016 Midwest Fruit Pest Management Guide. Take the time to scout your vineyard at a minimum of once per week. Grape plant tissues are most susceptible to infection when the tissue has extended wetting periods. However infection periods are also temperature dependent and an infection can occur when leaf wetness periods are as short as 2 hours at 77 F. Powdery Mildew Similar to downy mildew there are many fungicide options to control powdery mildew. These can be found on page 77 of the 2016 Midwest Fruit Pest Management Guide. Consider using Potassium salts if powdery mildew colonies have formed to burn out the colonies. It is important to follow-up with an application of protectant fungicide since potassium salts have no protectant activity.

10 10 Downy mildew susceptibility increases Leaf age increasing Young leaves are more susceptible to downy mildew than fully expanded mature leaves. Photo credit: Dean Volenberg

11 11 Japanese Beetles are Here!! Most University of Missouri Regional Horticulture Extension Specialists reported the presence of Japanese Beetles this week. What kind of year will it be. Typically during dry years the adult beetles have a difficult time emerging from the hard dry soil. Should a good rain occur be prepared for more adult beetle emergence. Focus initial scouting on vineyard border rows adjacent to grass areas. Missouri will be hosting the 41st American Society of Enology and Viticulture-Eastern Section (ASEV-ES) Conference and Symposium. The meeting will be in St. Louis, Missouri in July 18-21, The meeting includes a tour of Missouri wineries on the 18 th, research updates on the 19 th and 20 th and the 21 st will be dedicated to an industry oriented symposium on Adapting and Adopting: Future of Grape and Wine Production. Talks will be given by international experts relating to a wide range of viticulture and enology topics. Registration and additional information can be found at aseves.org Early Bird Registration Until July 1st

12 12 Cumulative Growing Degree Days for the Seven Grape Growing Regions of Missouri from April 1 to June 13, Region Location by County Growing Degree Days Year Average Augusta St. Charles Hermann Gasconade Ozark Highland Phelps Ozark Mountain Lawrence Southeast Ste. Genevieve Central Boone Western Ray Growing degree days at base 50 from April 1 to June 13, Data compiled from Useful and Useable at Click on link below to determine growing degree days in your area. To determine the number of growing degree days accumulated in your area since April 1, click this link Search for GDD at your location using this tool. Please scout your vineyards on a regularly scheduled basis in an effort to manage problem pests. This report contains information on scouting reports from specific locations and may not reflect pest problems in your vineyard. If you would like more information on IPM in grapes, please contact Dean Volenberg at or volenbergd@missouri.edu